In automotive engineering, in particular in the case of utility vehicles, vehicle electrical distribution systems having two different vehicle electrical distribution system voltages are conventional. Primarily, these are vehicle electrical distribution systems with a rated voltage of 12 V and vehicle electrical distribution systems with a rated voltage of 24 V. For both of these voltage ranges, normally solenoid valves are used whose coils differ from one another in terms of their resistance.
For manufacturers of utility vehicles which produce vehicles with both vehicle electrical distribution system variants, it may arise that solenoid valves for 12 V are incorrectly installed in vehicles with a vehicle electrical distribution system of 24 V or solenoid valves for 24 V are incorrectly installed in vehicles with a vehicle electrical distribution system of 12 V.
Previous anti-lock braking system or ABS control devices for utility vehicles in the vicinity of which solenoid valves under consideration in particular here are used have not been able to identify such faults, with the result that, in the case of solenoid valves for 24 V in a 12 V vehicle electrical distribution system, it may firstly arise that necessary valve activations do not take place and, secondly, in a case of solenoid valves for 12 V in a 24 V vehicle electrical distribution system, overload of the solenoid valves owing to excessively high currents can occur, which results in failure of said solenoid valves.
The fundamental reason for this consists in that previous configurations of ABS systems monitor end states of solenoid valves only for short circuits to ground, short circuits to the vehicle electrical distribution system supply voltage or battery voltage and/or for load interruptions. Identification of a fault in this case generally takes place by evaluation of voltage feedback. High-resistance loads are in this case only identified above very high resistance values, however.
Against this background, the invention is based on the object of providing a circuit arrangement for improved detection of a type of solenoid valve, with which the type of solenoid valve installed in an electrical distribution system of a vehicle can be determined in respect of corresponding voltage range of solenoid valve and vehicle electrical distribution system in the case of low resistance values to be considered.
In accordance with the invention, this object is achieved by the features described herein. Advantageous developments of the invention are the subject matter of the attached dependent claims.
The invention is based on the general concept of detecting a solenoid valve which has been incorrectly installed in a vehicle, in particular a utility vehicle, i.e. a solenoid valve whose voltage range does not match the voltage range of the electrical distribution system of the vehicle in which it is installed, via the resistance of the coils provided in each case in the solenoid valves of different voltage ranges. While coils of solenoid valves configured for 24 V, for example 24 V pressure control solenoid valves, have a resistance of typically approximately 16 ohms, for example, coils of solenoid valves configured for 12 V, for example, have a resistance of typically approximately 5 ohms. If a low measurement current is now impressed into each of the coils provided, the voltage resulting from this can be measured at the solenoid valve coil and evaluated via a microcontroller in a corresponding control device for determining the voltage rating range of the solenoid valve. The resistance of the solenoid valve coils can be calculated and determined from the measured voltage and the known impressed current.
In accordance with this general concept of the invention, the proposed circuit arrangement is advantageous insofar as the measurement circuit can be kept simple at low cost, but nevertheless provides measurement accuracy with a corresponding configuration such that it is possible to safely distinguish between at least two coil types over a specified voltage range, temperature range and tolerance range. A further advantage consists in that the configuration of the circuit arrangement is possible in such a way that even low impressed currents are sufficient for the coil type determination without any restriction to the actual level of a vehicle electrical distribution system rated voltage, with the result that the detection of the coil type is possible without electrically and/or mechanically activating the associated solenoid valve. The coil type determination can therefore take place in system-transparent fashion and as such in a manner which has no effect on remaining functions of the basic ABS system, for example, in other words without the ABS system being impaired or disrupted in any way.
The object is therefore achieved by a circuit arrangement for detecting a type of solenoid valve in vehicles, characterized by at least one solenoid valve which is incorporated into the circuit arrangement for the purpose of detecting the type of said solenoid valve and has at least one coil winding having a resistance which is of the typical order of magnitude for a predetermined vehicle electrical distribution system supply voltage; a constant current source, which is arranged so as to impress a predetermined measurement current into the at least one coil winding of the at least one solenoid valve; a current mirror circuit, which is arranged so as to generate a second voltage on a detection section of the circuit arrangement from a first voltage produced as a result of the impressed measurement current on the at least one coil winding of the at least one solenoid valve; wherein the second voltage produced on the detection section is passed out, on the detection section, directly to a microcontroller in a control device for determining the type of solenoid valve.
As a result, reliable identification of an operating voltage of a solenoid valve can be performed by a simple and inexpensive circuit configuration, which can also be integrated in an already existing control device or solenoid valve module, or can be configured as an additional module, wherein the identification only needs to be performed once during or after initialization of the remaining control electronics, and the identification in this case still remains without any functional effect on a respectively measured solenoid valve and therefore does not result in any further actuation or activation of the solenoid valve or other components in its range of action. In addition, a suitable configuration of the circuit configuration also enables a resistance measurement to ground potential, and a defective coil winding can also be determined via this resistance measurement, for example when the expected typical resistance value can no longer be determined, and also the temperature or change in temperature of the coil turn can be detected by such a resistance measurement.
The detected type of solenoid valve may be a vehicle electrical distribution system supply voltage for which the solenoid valve is configured, wherein the vehicle electrical distribution system supply voltage includes rated voltages of 12 V and/or 24 V and/or more than 24 V, and the solenoid valve is a pressure control solenoid valve for use in braking systems and/or traction control systems for a utility vehicle.
As a result, it is possible to conclude that there is a correct system state in safety-relevant parts of a utility vehicle in a quick and expedient manner by distinguishing between two possible variants and determining whether there is a faulty installation, for example after the manufacturer's production facility or else after time in a workshop, which can result in a non-response of a solenoid valve and/or in failure of a solenoid valve.
If the order of magnitude of the resistance of the coil winding of the solenoid valve for a rated voltage of 12 V is typically within a single-digit resistance range and, for a higher rated voltage distinguishable therefrom, is typically in a two-digit to three-digit resistance range, safe and nevertheless activation-less detection within the scope of the orders of magnitude of other system signals is possible.
The constant current source may include a transistor, which is connected to a respective resistance at the emitter, base and collector, with a voltage signal which is 5 V in the measurement state of the circuit arrangement being applied to the base connection of said transistor.
Further, the measurement current impressed by the constant current source into the at least one coil winding of the at least one solenoid valve may be configured such that solenoid valve type detection is reliably possible, but the flow of said measurement current does not yet result in functional activation of a respectively measured solenoid valve, and the measurement current is approximately 9 mA.
As a result, it is possible to generate and impress a suitable measurement current with a simple configuration and utilization of voltage potentials present in the entire system.
The current mirror circuit may include an operational amplifier, whose input voltage range up to its supply voltage is sufficient, a transistor and a second resistance, which forms the detection section, and the current mirror circuit transmits the first voltage to a first resistance, which is connected to the transistor towards the vehicle electrical distribution system supply voltage.
This arrangement makes it possible in a simple manner to transmit the voltage produced by the impressed measurement current at the coil of a measured solenoid valve to a circuit section on which said voltage can be received and evaluated by a microcontroller. Particular advantages result from the fact that a voltage produced at external points, for example on solenoid valves installed in wheel modules, can be converted in a suitable manner into an internal detection voltage, and this can additionally be matched to existing requirements by virtue of the configuration of the current mirror.
Advantageously, at least one first high-side switch for activating the coil of the at least one solenoid valve is provided in series with the at least one solenoid valve, a second switch, which is common for the at least one solenoid valve, is provided in parallel with the constant current source to ground potential, wherein said second switch is closed in the normal operating state, and a third switch for switchably impressing the constant current is provided at the constant current source, wherein, in a measurement operation state, the third switch is closed, the second switch is open, and the at least one first switch is closed.
This arrangement makes it possible, when a plurality of solenoid valves are provided, to implement and evaluate a separate and/or sequential measurement of individual solenoid valves by defined setting of the switching states of the individual switches by virtue of, for example, first the second and third switches being set to a state intended for the measurement and then the first switches which, in the case of a plurality of solenoid valves, are present in total as a plurality but in each case with only one on each individual solenoid valve being switched on/off or turned on successively, and therefore the impressed measurement current flowing in each case only through a or the desired coil(s) of the solenoid valves to be measured.
A sensitivity and/or a detection range of the circuit arrangement may be adjustable, wherein the resistance of the solenoid coils can be calculated via the transformation ratio U1/U2 of the first voltage to the second voltage and the impressed measurement current.
If the sensitivity and/or the detection range of the circuit arrangement is adjustable or capable of being switched over, it becomes possible to influence and possibly match the accuracy of the measurement and/or, if necessary, to measure a relatively large resistance difference between the resistance values of individual solenoid valve coils. Firstly, the circuit arrangement becomes suitable for universal use thereby, and secondly it becomes possible to replace individual solenoid valves with, for example, valves of another, for example newer, type with different coil resistance values without needing to make any changes to the remaining circuit arrangement. Since, in addition, the first voltage generated by the impressed measurement current or the value thereof converted after mirroring is detectable and the impressed measurement current itself is known, this enables a coil resistance detection without any notable loading of the system in respect of time and computation complexity.
The circuit arrangement may form part of an anti-lock braking system and/or part of a traction control system for utility vehicles.
In such safety-relevant sections of vehicles, the integration of an additional identification, in accordance with the invention, of the presence of a solenoid valve with the correct rating in respect of the vehicle electrical distribution system supply voltage is particularly advantageous because, for example, even in the case of system activation during end-of-line testing in the manufacturer's factory or once maintenance or repair work has been performed, for example, it is possible to avoid, by suitable signaling, a situation whereby a vehicle with parts which are unsuitable for operation at least initially is used on the road again. In other words, the risk of a fault owing to a) a non-response of a solenoid valve as a result of a lack of drivability and/or b) a partial system failure as a result of destruction of a solenoid valve after operation outside its specification and/or overloading becoming the responsibility of a driver of the utility vehicle is effectively reduced.
Specifically, overall the circuit arrangement according to the invention is in principle characterized by the fact that a battery is provided as vehicle electrical distribution system supply voltage, a first resistance and at least one first switch are connected at in each case one first connection to a high potential of the vehicle electrical distribution system supply voltage, a transistor is connected at an emitter connection to the first resistance, an operational amplifier is connected at an output thereof to a base connection of the transistor, an inverting input of the operational amplifier is connected to the first resistance and to the emitter connection of the transistor, a noninverting input of the operational amplifier is connected to a first connection of a second switch, a first connection of a third switch, and a second connection of the at least one solenoid valve, a first connection of the at least one solenoid valve is connected to a second connection of the at least one first switch, a collector connection of the transistor is connected to a first connection of a second resistance, a second connection of the third switch is connected to a first connection of the constant current source, and in each case a second connection of the second resistance, a second connection of the constant current source, and a second connection of the second switch are connected to a low potential of the vehicle electrical distribution system supply voltage, wherein the second voltage as measurement voltage is passed out to the microcontroller between the first connection of the second resistance and the collector connection of the transistor.
The invention will be described in more detail below using a exemplary embodiment of the circuit arrangement with reference to the drawing.